Exhaust emission control device

ABSTRACT

Provided are a hollow inner electrode constituted by an electrically conductive filter capable of capturing particulates, a cylindrical outer electrode circumferentially surrounding the electrode, a housing incorporated in a flow passage of exhaust and accommodating the electrodes and, a temperature sensor for detecting temperature of the exhaust and an electric discharge controller for controlling electric power to be distributed to the electrodes and on the basis of a detected value of the temperature sensor. When the temperature of the exhaust obtained by the temperature sensor is lowered, electric power necessary for generation of discharge plasma is distributed by the discharge controller to the electrodes and, thereby oxidizing the particulates captured by the electrode to reduce electricity consumption.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national stage entry of InternationalApplication No. PCT/JPO4/07611, filed on Jun. 2, 2004. The presentapplication also claims priority under 35 U.S.C. §119 to Japanese PatentApplication No. 2003-15767, filed Jun. 3, 2003, to Japanese PatentApplication No. 2003-157678, filed Jun. 3, 2003, and to Japanese PatentApplication No. 2003-160560, filed Jun. 5, 2003.

TECHNICAL FIELD

The present invention relates to an exhaust emission control device.

BACKGROUND ART

Particulates or particulate matter entrained in exhaust (burned gas ofdiesel oil) from a diesel engine is mainly constituted by carbonic sootand a soluble organic fraction (SOF) of high-boiling hydrocarbon andcontains a trace of sulfate (misty sulfuric acid fraction).

In order to suppress the particulates from being diffused intoatmosphere, conventionally a filter for capturing particulates isincorporated into an engine exhaust system.

An example of the particulate filter comprises a honeycomb core made ofceramics such as cordierite and having a number of passagescompartmentalized by porous thin walls, exhaust from an engine flowingthrough the passages.

In the above-mentioned particulate filter, alternate ones of theparallel passages have plugged one ends so as to guide the exhaust tounplugged one ends of the gas passages adjacent thereto; the passagesthrough which the exhaust flows have the plugged other ends so as toconnect unplugged other ends of the gas passages adjacent thereto to amuffler.

Thus, the particulates entrained in the exhaust are captured by theporous thin walls and only the exhaust passing through the walls isdischarged to the atmosphere.

The particulates attached to the thin walls will spontaneously ignite tobe oxidized when an engine operating status is shifted to a region withincreased exhaust temperature.

However, for example, in a shuttle-bus running mainly on city roads withgenerally lower running speeds, there is few chance to continue anengine operational status capable of obtaining exhaust temperaturesuited for oxidation treatment of the particulates. As a result, acaptured particulate amount will exceed an oxidized amount, leading toclogging of the porous thin walls.

Thus, recently, a plasma assisted exhaust emission control device (gastreatment reaction vessel) has been proposed which can oxidizeparticulates even if exhaust temperature is low (see, for example,Reference 1).

In this exhaust emission control device, inner and outer electrodes eachin the form of drilled stainless cylinders are coaxially arranged in achamber. A gap between the electrodes is charged with dielectrics in theform of pellets so as to allow the exhaust to pass. The exhaust from theengine is guided to a gap between the chamber and the outer electrode.

Thus, the particulates entrained in the exhaust supplied from betweenthe chamber and the outer electrode to the pellet charged layer areattached to the pellets and only the exhaust passing through the layeris discharged to the atmosphere.

Higher voltage is applied across the electrodes to generate dischargeplasma and excite the exhaust, so that unburned hydrocarbon, oxygen andnitrogen monoxide are activated into oxygen-containing hydrocarbon,ozone and nitrogen dioxide, respectively.

Thus, even with lower exhaust temperature, the particulates attached tothe pellets will spontaneously ignite to be oxidized.

[Reference 1] JP 2002-501813A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, constant application of higher voltage to the electrodes in theconventional plasma assisted exhaust emission control device will resultin excessively consumed electricity.

When the electric power for generation of electric discharge isalternating current (AC), an equivalent circuit is a circuit in which AChigh voltage is applied to a condenser constituted by inner and outerelectrodes. Capacitance of the condenser may vary depending upon forexample the captured particulate amount and/or the exhaust components;thus, it is assumed that reactance of the circuit varies to cause phaselag between voltage and current waveforms, resulting in lowering ofpower factor.

Furthermore, it has not been practiced to actually decide how muchparticles are captured in the conventional plasma assisted exhaustemission control device.

The invention was made in view of the above and has its object toprovide an exhaust emission control device with less electricityconsumption which can avert lowering of power factor due to the capturedparticulate amount and/or the exhaust components and which can decide anamount of particulates captured.

Means or Measure for Solving the Problems

In order to attain the above object and according to a first aspect ofthe invention, provided are electrodes for generating plasma in exhaustthrough electric discharge, a capturing body for capturing particulatesentrained in the exhaust, a temperature sensor for detecting temperatureof the exhaust and an electric discharge controller for controllingelectric power to be distributed to the electrodes on the basis of adetected value of said temperature sensor.

According to a second aspect of the invention, provided are electrodesfor generating plasma in exhaust through electric discharge, a capturingbody for capturing particulates entrained in the exhaust, capturedamount deciding means for deciding amount of the particulates capturedby said capturing body and an electric discharge controller forcontrolling electric power to be distributed to the electrodes on thebasis of a calculated value of said captured amount deciding means.

According to a third aspect of the invention, provided are a capturingcell for capturing particulates between a pair of electrodes arranged ina flow passage of exhaust, high voltage output means for distributing ACpower for electric discharge to the electrodes, a plurality of inductorsparallelly connectable between said high voltage output means and saidelectrodes and inductance control means for detecting a phase of the ACpower distributed to the electrodes and for connecting proper one orones of the inductor to the high voltage output means and to theelectrodes so as to reduce reactance variation.

According to a fourth aspect of the invention, provided are a capturingcell for capturing particulates between a pair of electrodes arranged ina flow passage of exhaust, high voltage output means for distributing ACpower for electric discharge to the electrodes, a variable inductorarranged between said high voltage output means and said electrodes andinductance control means for detecting a phase of the AC powerdistributed to the electrodes and for controlling the variable inductorso as to reduce reactance variation.

According to a fifth aspect of the invention, provided are a capturingcell for capturing particulates between a pair of electrodes arranged ina flow passage of exhaust, high voltage output means for distributing ACpower for electric discharge to the electrodes, a plurality of variableinductors parallelly connectable between said high voltage output meansand said electrodes and inductance control means for detecting a phaseof the AC power distributed to the electrodes and for controllingvariable inductance through connection of proper one or ones of thevariable inductors to the high voltage output means and to theelectrodes so as to reduce reactance variation.

According to a sixth aspect of the invention, provided are one and theother electrodes, said one electrode being constituted by anelectrically conductive filter capable of capturing particulates andarranged in a flow passage of exhaust, the other electrode beingarranged adjacent to said one electrode, an electric dischargecontroller for distributing electric power for generation of electricdischarge to the electrodes and captured amount deciding means fordetecting resistance value upon power distribution to said one electrodeto decide a particulate amount.

According to a seventh aspect of the invention, provided are one and theother electrodes, said one electrode being constituted by anelectrically conductive filter capable of capturing particulate andarranged in a flow passage of the exhaust, the other electrode beingarranged adjacent to said one electrode, an electric dischargecontroller for distributing electric power for generation of electricdischarge to the electrodes and captured amount deciding means fordetecting current value upon power distribution to said one electrode todecide a particulate amount.

According to an eighth aspect of the invention, provided are one and theother electrodes, said one electrode being constituted by anelectrically conductive filter capable of capturing particulates andarranged in a flow passage of exhaust, the other electrode arrangedadjacent to said one electrode, an electric discharge controller fordistributing electric power for generation of electric discharge to theelectrodes and captured amount deciding means for detecting voltagevalue upon power distribution to said one electrode to decide aparticulate amount.

In the first aspect of the invention, when the exhaust temperaturedetected by the temperature sensor is lower than a setting value,electric power necessary for generation of discharge plasma isdistributed by the discharge controller to the electrodes, therebyoxidizing the particulates captured by the capturing body.

In the second aspect of the invention, when the particulate amountestimated by the captured amount deciding means exceeds a setting value,electric power necessary for generation of discharge plasma isdistributed by the discharge controller to the electrodes, therebyoxidizing the particulates captured by the capturing body.

In the third aspect of the invention, the inductance control means fordetecting the phase of AC power distributed to the electrodes in thecapturing cell connects proper one or ones of the inductances to thehigh voltage output means and to the electrode so as to reduce reactancevariation.

In the fourth aspect of the invention, the inductance control means fordetecting the phase of AC power distributed to the electrodes in thecapturing cell controls the variable inductance so as to reducereactance variation.

In the fifth aspect of the invention, the inductance control means fordetecting the phase of AC power distributed to the electrodes in thecapturing cell connects proper one or ones of the variable inductancesto the high voltage output means and to the electrodes and controls saidvariable inductances so as to reduce reactance variation.

In the sixth aspect of the invention, when the particulates captured bythe one electrodes constituted by the electrically conductive filter areincreased, resistant value upon power distribution to the one electrodeis decreased accordingly.

In the seventh aspect of the invention, when the particulates capturedby the one electrode constituted by the electrically conductive filterare increased, current value upon power distribution to the oneelectrode is increased accordingly.

In the eighth aspect of the invention, when the particulates captured bythe one electrode constituted by the electrically conductive filter areincreased, voltage value upon power distribution to the one electrode isdecreased accordingly.

EFFECTS OF THE INVENTION

According to an exhaust emission control device of the invention, thefollowing various excellent meritorious effects may be obtained.

-   (1) In the first aspect of the invention, when the exhaust    temperature detected by the temperature sensor is lower than the    setting value, electric power necessary for generation of discharge    plasma is distributed by the discharge controller to the electrodes    to thereby oxidize the particulates captured by the capturing body,    so that electric power consumption is reduced to enhance energy use    efficiency.-   (2) In the second aspect of the invention, when the captured    particulate amount estimated by the captured particulate amount    deciding means exceeds the setting value, electric power necessary    for generation of discharge plasma is distributed by the discharge    controller to the electrodes to thereby oxidize the particulates    captured by the capturing body, so that electric power consumption    is reduced to enhance energy use efficiency.-   (3) In the third aspect of the invention, on the basis of the phase    of the AC power, the inductance control means connects proper one or    ones of the inductors to the high voltage output means and to the    electrodes to thereby reduce reactance variation, so that lowering    of power factor due to the captured particulate amount and/or the    exhaust components can be averted to enhance energy efficiency.-   (4) In the fourth aspect of the invention, on the basis of the phase    of the AC power, the inductance control means controls the variable    inductor to thereby reduce reactance variation, so that lowering of    power factor due to the captured particulate amount and/or the    exhaust components can be averted to enhance energy efficiency.-   (5) In the fifth aspect of the invention, on the basis of the phase    of the AC power, the inductance control means connects proper one or    ones of the variable inductors to the high voltage output means and    to the electrodes and controls said variable inductors to thereby    reduce reactance variation, so that lowering of power factor due to    the captured particulate amount and/or the exhaust components can be    averted to enhance energy efficiency.-   (6) In the sixth aspect of the invention, when the particulates    captured by the one electrode constituted by the electrically    conductive filter are increased, resistance value upon power    distribution to the one electrode is decreased accordingly, so that    decided is the captured particulate amount to thereby efficiently    distribute electric power for electric discharge to the electrodes.-   (7) In the seventh aspect of the invention, when the particulates    captured by the one electrode constituted by the electrically    conductive filter are increased, current value upon power    distribution to the one electrode is increased accordingly, so that    decided is the captured particulate amount to thereby-efficiently    distribute electric power for electric discharge to the electrodes.-   (8) In the eighth aspect of the invention, when the particulates    captured by the one electrode constituted by the electrically    conductive filter are increased, voltage value upon power    distribution to the one electrode is decreased accordingly, so that    decided is the captured particulate amount to thereby efficiently    distribute electric power for electric discharge to the electrodes.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be described with reference to thedrawings.

Embodiment 1

FIGS. 1 and 2 show a first embodiment of an exhaust emission controldevice according to the invention. This exhaust emission control devicecomprises a capturing cell 1, a temperature sensor 2 and an electricdischarge controller 3.

The cell 1 comprises a housing 4 incorporated in a flow passage ofexhaust G to be purified, a hollow inner electrode 5 constituted by anelectrically conductive filter capable of capturing particulates andcoaxially arranged within the housing 4, a cylindrical outer electrode 6arranged within the housing 4 to circumferentially surround theelectrode 5 and a dielectric 7 made of ceramics for lining of an innersurface of the outer electrode 6.

Moreover, a particulate filter using for example cordierite isincorporated in the flow passage of the exhaust G separately from thecapturing cell 1.

The above-mentioned electrically conductive filter may be, for example,fibrous metal laminated and sintered into integrity, sintered body ofmetallic powder, fine metallic mesh laminated and sintered intointegrity or metallic powder carried by fine metallic mesh throughsintering; any of them may capture the particles while ensuring passingof the gas.

The inner electrode 5 has closed upstream and open downstream ends in adirection of travel of the exhaust G. An annular insulant 8 is arrangeddownstream of the electrodes 5 and 6 in the direction of travel of theexhaust G so as to contact whole circumferences of the ends of theelectrodes 5 and 6.

Thus, the exhaust G from an engine (not shown) flows into a gap 9between an outer surface of the inner electrode 5 and an inner surfaceof the dielectric 7 in the capturing cell 1, passes through theelectrode 5 from outward to inward thereof and flows via the inner spacein the electrode 5 into a muffler (not shown) downstream of the cell 1,the particulates being captured by the electrode 5 which is theelectrically conductive filter.

The sensor 2 is arranged at an exhaust inflow port of the housing 4 todetect a temperature of the exhaust G.

The discharge controller 3 is connected to the temperature sensor 2 andto an in-vehicle power supply 10 such as alternator.

The discharge controller 3 is constructed to conduct control (see FIG.2) such that electric power to be distributed to the electrodes 5 and 6is set to have a discharge plasma amount generated enough for oxidationof particulates when a value (temperature of the exhaust G) detected bythe sensor 2 is in a range not reaching spontaneous ignition of theparticulates and that electric power to be delivered to the electrodes 5and 6 is reduced to suppress the discharge plasma amount generated whenthe value detected by the sensor 2 is in a range reaching the oxidationof the particulates.

The above-mentioned control of electric power to be distributed dependson temperature of the exhaust G and may be, for example, in the form of

-   a. increase/decrease of time for power distribution to the    electrodes 5 and 6 per unit time,-   b. increase/decrease of voltage applied to the electrodes 5 and 6,-   c. increase/decrease of current applied to the electrodes 5 and 6,-   d. distribution of AC to the electrodes 5 and 6 and    increase/decrease of frequency thereof,-   e. distribution of DC to the electrodes 5 and 6 and    increase/decrease of duty ratio thereof or-   f. increase/decrease of waveform risetime in item e above.

Thus, when the temperature of the exhaust G is low, for example ozoneand/or oxygen radical is generated by the discharge controller 3 throughdischarge plasma to oxidize the particulates to thereby reduce electricpower consumption.

Embodiment 2

FIGS. 3 to 5 show a second embodiment of an exhaust emission controldevice according to the invention. This exhaust emission control devicecomprises a capturing cell 1, captured amount deciding means 11 and anelectric discharge controller 12; the capturing cell 1 and an in-vehiclepower supply 10 are structurally of the same as those in FIG. 1.

The deciding means 11 is constructed such that it measures parameterssuch as an inner pressure in the housing 4 and electric characteristicsof the inner electrode 5 (voltage, current and resistance values uponpower distribution) and calculates a captured particulate amount on theelectrode 5 at the time on the basis of interrelation between measuredparameter values and a preliminarily measured, captured particulateamount on the electrode 5.

The discharge controller 12 is connected to the in-vehicle power supply10 and to the captured amount deciding means 11.

The discharge controller 12 is constructed to conduct control (see FIGS.4 and 5) such that electric power to be distributed to the electrodes 5and 6 is increased to increase a discharge plasma amount generateddepending upon the captured particulate amount when the capturedparticulate amount calculated by the deciding means 11 exceeds a presetrange.

The above-mentioned control of electric power to be distributed dependson captured particulate amount and may be, for example, in the form of

-   g. increase/decrease of time for power distribution to the    electrodes 5 and 6 per unit time,-   h. increase/decrease of voltage applied to the electrodes 5 and 6,-   i. increase/decrease of current applied to the electrodes 5 and 6,-   j. distribution of AC to the electrodes 5 and 6 and    increase/decrease of frequency thereof,-   k. distribution of DC to the electrodes 5 and 6 and    increase/decrease of duty ratio thereof or-   l. increase/decrease of waveform risetime in item k above.

Thus, only when the captured particulate amount on the electrode 5 isincreased, for example ozone and/or oxygen radical is generated by thedischarge controller 12 through discharge plasma to oxidize theparticulates to thereby reduce electric power consumption.

The electrodes for generation of discharge plasma may be in the shape ofparallel plates or lattice; pellets or honeycomb of ceramics may beutilized for the particulate capturing body.

Embodiment 3

FIG. 6 shows a third embodiment of an exhaust emission control deviceaccording to the invention. This exhaust emission control devicecomprises a capturing cell 21, high voltage output means 22 foroutputting AC power for electric discharge, a plurality of inductorsL1-L6 and inductance control means 23.

The capturing cell 21 comprises a pair of electrodes 24 and 25 arrangedin a flow passage of the exhaust G to be purified and a dielectric 26for lining of the one electrode 24, the other electrode 25 beingconstituted by an electrically conductive filter capable of capturingparticulates.

The electrodes 24 and 25 may be of a shape such as cylinder, parallelplates or lattice.

The electrically conductive filter may be fibrous metal laminated andsintered into integrity, sintered body of metallic powder, fine metallicmesh laminated and sintered into integrity or metallic powder carried byfine metallic mesh through sintering; any of them may capture theparticulates while ensuring passing of the gas. The particulates may bealso attached to a surface of the dielectric 26.

The inductors L1-L6 are serially connected to switches S1-S6,respectively, these serial combinations of the inductors L1-L6 with theswitches S1-S6, respectively, are parallelly connected to the highvoltage output means 22 and to the electrode 25 in the capturing cell21.

With at least one of the switches S1-S6 being closed, the inductancecontrol means 23 detects phase lag between voltage and current waveformsof AC distributed by the high voltage output means 22 to the electrodes24 and 25, calculates inductance necessary for reducing reactancevariation at the time, and closes any or some of the switches S1-S6accompanied with the inductors L1-L6, respectively, to be connected tothe circuit so as to obtain inductance similar or equal to thecalculated vale by singularly any of the inductors L1-L6 or bycombination thereof.

More specifically, five alternative inductance values may be obtained incombination of opening and closing of the switches S1-S6 when theinductances of the inductors L1-L6 are all the same; maximum 35inductance values may be obtained in combination of opening and closingof the switches S1-S6 when the inductances of the inductors L1-L6 aredifferent.

Thus, the inductance control means 23 connects proper one or ones of theinductors L1-L6 to the high voltage output means 22 and to theelectrodes 24 and 25 so as to reduce reactance variation, so thatlowering of power factor due to the captured particulate amount and/orthe exhaust components can be averted so as to enhance energyefficiency.

As a result, when the amount of the particulates captured in thecapturing cell 21 becomes excessive, AC power is delivered by the highvoltage output means 22 to the electrodes 24 and 25 to generatedischarge plasma, whereby the particulates are reliably oxidized by, forexample, ozone and/or oxygen radical.

Embodiment 4

FIG. 7 shows a fourth embodiment of an exhaust emission control deviceaccording to the invention. This exhaust emission control devicecomprises a capturing cell 21, high voltage output means 22, a variableinductor L7 and inductance control means 27, the capturing cell 21 andthe high voltage output means 22 being structurally of the same as thosein FIG. 6.

The inductance control means 27 is constructed such that it detectsphase lag between voltage and current waveforms of AC delivered by thehigh voltage output means 22 to the electrodes 24 and 25, calculatesinductance necessary for reducing reactance variation and controls thevariable inductor L7 so as to obtain inductance similar or equal to thecalculated value.

Thus, obtained is the inductance value in a range depending upon designcondition of the variable inductor L7.

In this manner, the inductance control means 27 controls the variableinductor L7 so as to reduce reactance variation, so that lowering ofpower factor due to the captured particulate amount and/or the exhaustcomponents to enhance energy efficiency.

Thus, when the amount of particulates captured in the capturing cell 21becomes excessive, AC power is distributed by the high voltage outputmeans 22 to the electrodes 24 and 25 to generate discharge plasma,whereby the particulates can be reliably oxidized through ozone and/oroxidized radical.

Embodiment 5

FIG. 8 shows a fifth embodiment of an exhaust emission control deviceaccording to the invention. This exhaust emission control devicecomprises a capturing cell 21, high voltage output means 22, variableinductors L8 and L9 and inductance control means 28; the capturing cell21 and high voltage output means 22 being structurally of the same asthose in FIG. 6.

The variable inductors L8 and L9 are serially connected to the switchesS8 and S9, respectively; these serially interconnected variableinductors L8 and L9 and switches S8 and S9 are connected parallelly tothe high voltage output means 22 and to the electrode 25 in thecapturing cell 21.

The inductance control means 28 is constructed such that, with at leastone of the switches S8 and S9 being closed, the means 28 detects phaselag between voltage and current waveforms of AC distributed by the highvoltage output means 22 to the electrodes 24 and 25, calculatesinductance necessary for reducing reactance variation at the time,closes either or both of the switches S8 and S9 accompanied with thevariable inductors L8 and L9 to be connected to the circuit so as toobtain inductance similar or equal to the calculated value singularly bythe variable inductor L8 or L9 or by combination thereof and controlsthe variable inductors L8 and L9.

Thus, inductance value will be obtained in a range depending upon eitherof the design conditions of the variable inductors L8 and L9 orcombination thereof.

In this way, the inductance control means 28 controls the variableinductors L8 and L9 so as to reduce reactance variation, so thatlowering of power factor due to the captured particulate amount and/orthe exhaust components can be averted to enhance energy efficiency.

Thus, when the captured particulate amount in the capturing cell 21becomes excessive, Ac power is delivered by the high voltage outputmeans 22 to the electrodes 24 and 25 to generate discharge plasma,whereby the particulates can be reliably oxidized through ozone and/oroxygen radical.

Embodiment 6

FIGS. 9 and 10 show a sixth embodiment of an exhaust emission controldevice according to the invention. This exhaust emission control devicecomprises a capturing cell 31, captured amount deciding means 32 and anelectric discharge controller 33.

The capturing cell 31 comprises a housing 34 incorporated in a flowpassage of exhaust G to be purified, a hollow inner electrode 35constituted by an electrically conductive filter capable of capturingparticulates and coaxially arranged within the housing 34, a cylindricalouter electrode 36 arranged within the housing 34 to circumferentiallysurround the inner electrode 35 and a dielectric 37 made of for exampleceramics for lining of an inner surface of the outer electrode 36.

Moreover, a particulate filter using for example cordierite isincorporated in the flow passage of the exhaust G separately from thecapturing cell 31.

The electrically conductive filter may be fibrous metal laminated andsintered into integrity, sintered body of metallic powder, fine metallicmesh laminated and sintered into integrity or metallic powder carried byfine metallic mesh through sintering; any of them may capture theparticulates while ensuring passing of the gas.

The inner electrode 35 has upstream closed and downstream open ends in adirection of travel of the exhaust G; an annular insulant 38 is arrangeddownstream of the electrodes 35 and 36 in the direction of travel of theexhaust G so as to contact whole circumference of the ends of theelectrodes 35 and 36.

Thus, the exhaust G from an engine (not shown) flows into a gap 39between an outer surface of the inner electrode 35 and an inner surfaceof the dielectric 37 in the capturing cell 31, pass the electrode 35from outward to inward thereof and flows via an interior space in theelectrode 35 to a muffler (not shown) downstream of the capturing cell31; the particulates are captured by the electrode 35 which is theelectrically conductive filter.

The deciding means 32 is constructed such that it measures resistancevalue of the electric circuit through power distribution of the innerelectrode 35 by current for searching, and decides whether the capturedparticulate amount on the inner electrode 35 at the time exceeds asetting value or not so as to output a signal, on the basis ofinterrelation between said resistance value as parameter and apreliminarily measured captured amount of particulates on the electrode35 and in accordance with steps S10-S15 in FIG. 10.

Alternatively, the measured resistance value may be compared with aplurality of setting values to assume a degree of the capturedparticulate amount on the inner electrode 35. When no power distributionof current for searching is conducted, the deciding means 32 is adaptedto be disconnected from the above-mentioned electric circuit.

The main component of the particulates is carbon (dielectric). As aresult, the more the particulate amount captured by the electrode 35 is,the lower the resistance value as determining factor for the capturedamount is.

Thus, by measuring resistance value of the electrode 35 at a properinterval upon no electric discharge, decided is whether the innerelectrode 35 has captured a setting amount of particulates or not.

The discharge controller 33 is connected to the above-mentioned decidingmeans 32 and to an in-vehicle power supply 40 such as alternator.

The discharge controller 33 is constructed such that, when it receives adecision signal on excessively captured particulate amount from thedeciding means 32, it delivers electric power to the electrodes 35 and36 to generate discharge plasma.

Thus, when the amount of the particulates captured by the innerelectrode 35 becomes excessive, the discharge controller 33 generatesdischarge plasma to oxidize the particulates through, for example, ozoneand/or oxygen radical.

Embodiment 7

FIGS. 11 and 12 show a seventh embodiment of an exhaust emission controldevice according to the invention. This exhaust emission control devicecomprises a capturing cell 31, captured amount deciding means 41 and adischarge controller 33, the capturing cell 31, the discharge controller33 and the in-vehicle power supply 40 being structurally of the same asthose in FIG. 9.

The deciding means 41 is constructed such that it measures current valueof the electric circuit through power distribution of the electrode 35by current for searching, and decides whether the captured particulateamount on the electrode 35 at the time exceeds a setting value or not tooutput a signal, on the basis of interrelation between said currentvalue as parameter and a preliminarily measured captured amount ofparticulates on the inner electrode 35 and in accordance with stepsS20-S25 in FIG. 12.

Alternatively, the measured current value may be compared with aplurality of setting values to assume a degree of the capturedparticulate amount on the inner electrode 35. When no power distributionof current for searching is conducted, the deciding means 41 is adaptedto be disconnected from the above-mentioned electric circuit.

The main component of the particulates is carbon (dielectric). As aresult, the more the amount of particulates captured by the electrode 35is, the higher the current value as deciding factor for the capturedamount is.

Thus, by measuring current value of the electrode 35 at proper intervalupon no electric discharge, decided is whether the electrode 35 hascaptured a setting amount of particulates or not.

The discharge controller 33 is connected to the above-mentioned decidingmeans 41 and to the in-vehicle power supply 40.

Thus, when the amount of the particulates captured by the electrode 35becomes excessive, the discharge controller 33 generates dischargeplasma to oxidize the particulates through, for example, ozone and/oroxygen radical.

Embodiment 8

FIGS. 13 and 14 show an eighth embodiment of an exhaust emission controldevice according to the invention. This exhaust emission control devicecomprises a capturing cell 31, captured amount deciding means 42 and anelectric discharge controller 33, the capturing cell 31, the dischargecontroller 33 and an in-vehicle power supply 40 being structurally ofthe same as those in FIG. 9.

The deciding means 42 is constructed such that it measures voltage valueof the electric circuit through power distribution of the electrode 35by current for searching and decides whether the captured particulateamount on the electrode 35 at the time exceeds a setting value or not soas to output a signal, on the basis of interrelation between saidvoltage value as parameter and a preliminarily measured captured amountof the particulates on the electrode 35 and in accordance with stepsS30-S35 in FIG. 14.

Alternatively, the measured voltage value may be compared with aplurality of setting values to assume a degree of the capturedparticulate amount on the electrode 35. When no power distribution ofcurrent for searching is conducted, the deciding means 42 is adapted tobe disconnected from the above-mentioned electric circuit.

The main component of the particulates is carbon (dielectric). As aresult, the more the amount of particulates captured by the electrode 35is, the more prominently the voltage value as deciding factor for thecaptured amount is lowered.

Thus, by measuring the voltage value of the electrode 35 at properinterval upon no electric discharge, decided is whether the electrode 35has captured the setting amount of particulates or not.

The discharge controller 33 is connected to the above-mentioned decidingmeans 42 and to the in-vehicle power supply 40.

Thus, when the amount of the particulates captured by theinner-electrode 35 becomes excessive, the discharge controller 33generates discharge plasma to oxidize the particulates through, forexample, ozone and/or oxygen radical.

The electrodes for generation of discharge plasma may be in the shape ofopposed plates or lattice.

It is to be understood that an exhaust emission control device accordingto the invention is not limited to the above-mentioned embodiments andthat various changes and modifications may be effected without leavingthe gist of the invention.

INDUSTRIAL APPLICABILITY

An exhaust emission control device according to the invention may beapplicable to various types of vehicles.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1. A conceptual diagram showing a first embodiment of an exhaustemission control device according to the invention.

FIG. 2. A graph showing an example of relationship between exhausttemperature and generated plasma amount.

FIG. 3. A conceptual diagram showing a second embodiment of an exhaustemission control device according to the invention.

FIG. 4. A graph showing an example of relationship between capturedparticulate amount and generated plasma amount.

FIG. 5. A graph showing another example of relationship between capturedparticulate amount and generated plasma amount.

FIG. 6. A conceptual diagram showing a third embodiment of an exhaustemission control device according to the invention.

FIG. 7. A conceptual diagram showing a fourth embodiment of an exhaustemission control device according to the invention.

FIG. 8. A conceptual diagram showing a fifth embodiment of an exhaustemission control device according to the invention.

FIG. 9. A conceptual diagram showing a sixth embodiment of an exhaustemission control device according to the invention.

FIG. 10. A flowchart concerning FIG. 9.

FIG. 11. A conceptual diagram showing a seventh embodiment of an exhaustemission control device according to the invention.

FIG. 12. A flowchart concerning FIG. 11.

FIG. 13. A conceptual diagram showing an eighth embodiment of an exhaustemission control device according to the invention.

FIG. 14. A flowchart concerning FIG. 13.

EXPLANATION OF THE REFERENCE NUMERALS

-   2 temperature sensor-   3 discharge controller-   5 inner electrode (capturing body)-   6 outer electrode-   11 captured amount deciding means-   12 discharge controller-   21 capturing cell-   22 high voltage output means-   23, 27 and 28 inductance control means-   24 and 25 electrode-   32 captured amount deciding means-   33 discharge controller-   35 inner electrode (one electrode)-   36 outer electrode (the other electrode)-   41 and 42 captured amount deciding means-   G exhaust-   L1-L6 inductor-   L7-L9 variable inductor

1. An exhaust emission control device comprising a capturing cell forcapturing particulates between a pair of electrodes arranged in a flowpassage of exhaust, high voltage output means for distributing AC powerfor electric discharge to the electrodes, a plurality of variableinductors parallelly connectable between said high voltage output meansand said electrodes and inductance control means for detecting a phaseof AC power distributed to the electrodes and for controlling variableinductance through connection of proper one or ones of the variableinductors to the high voltage output means and to the electrodes so asto reduce reactance variation.